Tolkien makes a somewhat inconsistent use of the diaeresis to remind his readers that the vowels in the High-elven combinations EA, EO, OA, OE are dissyllabic (i.e. not diphthongs) and that final E is never mute in Quenya. This mark has no counterpart in Elvish script and is thus strictly redundant: with or without the diaeresis the intended pronunciation is the same.
Furthermore, it is in present-day English an obsolescent symbol, with which even native speakers often seem unfamiliar. It is frequently confused with the umlaut, used in e.g. Finnish, German, and Swedish as a means to represent independent vowel sounds. (For example, Bar and Bär are phonemically different words in German.) To many people, spellings like Eärendil, Eöl will therefore be misleading rather than helpful.
For these reasons, we feel that the best policy when writing Elvish is to omit the diaereses entirely (except of course in verbatim quotations from Tolkien's texts).
One technical issue often comes up when Tolkien's works is discussed: how should diacritical signs be represented? HTML has some, but not all, and many mail systems only accept plain vanilla 7-bit ASCII.
This has been discussed in the Mellonath Daeron too. We have tried to design a system which works in ASCII, is easy to remember and graphically intuitive.
This is what we came up with. We would like to offer this as a suggestion for a "Net Standard".
Not all these signs can be expressed in HTML either. Where possible, this table contains examples how to write the letter 'a' with the different diacritics.
|breve (cup above)
|macron and breve